Transpiration cooled turbine rotor blade

ABSTRACT

A transpiration cooled turbine rotor blade, having a solid strut with spanwise and chordwise lands on the surface, thereof, and a porous sheath attached to the lands, and having provision for metering desired amounts of cooling air to selected portions of the blade surface in view of the centrifugal pumping action of the blade.

ilnited Mates Patent De 1*eo [54] T RANSPWATTON COULED TURBHNE ROTOR BLADE [72] Inventor: Angelo De Feo, Totowa Boro, NJ.

[73] Assignee: Curtiss-Wright Corporation [22] Filed: July 27, 1970 [21] Appl. No.: 58,478

[52] US. Cl, ..416/97, 416/231 [51] Int. Cl ..F01d 5/13 [58] Field of Search ..416/97,231,92, 96

[56] References Cited UNITED STATES PATENTS 2,946,681 7/1960 Probst et a1. ..416/23 UX 3,067,982 12/1962 Wheeler ..416/231 X [451 Apr. 1%, 1972 3,240,468 3/1966 Watts et al. ..416/97 X 3,402,914 9/1968 Kump et a1. ..416/23l 3,468,513 9/1969 Schmitz ..416/97 UX FOREIGN PATENTS on APPLICATIONS 1,801,475 4/1970 Germany ..416/96 Primary Examiner-Everette A. Powell, Jr. Attorney-Raymond P. Wallace and Victor D. Behn [5 7] ABSTRACT A transpiration cooled turbine rotor blade, having a solid strut with spanwise and chordwise lands on the surface, thereof, and a porous sheath attached to the lands, and having provision for metering desired amounts of cooling air to selected portions of the blade surface in view of the centrifugal pumping action of the blade.

3 Claims, 7 Drawing Figures PATENTEBAPR 18 I972 SHEET 10F 2 TIP END Z K :600F w LLJ I Q 1 I (I1 HUB END TEMPERATURE INCREASE- f I l I I I l l l l I l I I I g I,

I w Z INVENTOR.

ANGELO DEFEO AGENT PATENTEUAPR 18 1972 SHEET 2 OF 2 FIG. 4

FIG. 3

FIG. 5

INVENTOR.

ANGELO D'E- F'EO AGENT TRANSIIRATION COOlLlED 1 INIE ROTOR BLADE BACKGROUND OF THE INVENTION Transpiration cooled stator blades are known in the prior art, such as that of U.S. Pat. No. 3,240,468, having'a hollow strut covered with a porous sheath attached to lateral and transverse lands on the surface of the strut defining discrete recesses. Cooling air is supplied to the interior of the strut, and is metered to each of the recesses through apertures of varying sizes through the wall of the strut. This system works well enough with stator blades, which can have a hollow strut and where the pressure inside the hollow strut can be maintained at a constant value for given operating conditions.

In rotor blades hollow struts have not been successful, owing to the great centrifugal force produced by rotation, which requires a strut of higher strength, and which also produces a centrifugal pumping action of the air supplied at the root, with a consequent increase of air pressure toward the radially outward direction. Transpiration cooled rotor blades of a different type are known, such as that of U.S. Pat. No. 3,402,914, having a solid strut with surface lands extending from root to tip and defining longitudinal channels, with a porous sheath attached to the lands, and air supplied to the channels under the sheath at the root end. The porosity of the sheath is reduced in selected areas by coating or impregnating it with powdered sintered metal. However, such sintered patches cause surface discontinuities which disturb the gas flow, control of their degree of porosity is difficult, they are subject to spallation and other damage, and no provision can be made for the centrifugal pumping action on the air in the longitudinal channels, by reason of which the air pressure at the tip end of the blade is greatly increased. The present invention overcomes these limitations of the prior art.

SUMMARY OF THE INVENTION The present invention provides a turbine rotor blade having a solid strut with surface lands in both the longitudinal and transverse directions, defining discrete recesses on the surface of the strut, which is covered by a sheath of porous material. Cooling air under pressure is supplied through passages under the sheath at the root portion to those recesses nearest the root portion of the blade, and successively to further recesses through metering apertures in the lands which separate the recesses. The entrance passages in the root, distributed across the chord of the blade, are appropriately sized to supply the desired amount of air in the chordwise direction, and the apertures in the lands are appropriately sized to control the air pressure from one recess to another, all with regard to temperature and pressure profiles of the gas in the passages between the blades, and to the spanwise increase in air pressure due to centrifugal pumping by the blades.

It is therefore an object of this invention to provide a transpiration cooled turbine rotor blade having cooling air metered to various portions of the blade in accordance with local cooling requirements.

It is another object to provide a transpiration cooled turbine rotor blade wherein the effect of centrifugal pumping of cooling air is balanced by metering arrangements.

Other objects and advantages will become apparent on reading the following specification in connection with the annexed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph of a typical distribution of the gas temperatures along the span of a turbine rotor blade;

FIG. 2 is a graphical representation of a typical variation of gas pressure around a turbine rotor blade at a selected distance along the span;

FIG. 3 is an elevation of the concave side of a turbine rotor blade, with the porous skin in cross-section;

FIG. 4 is a similar view of the convex side of the blade;

FIG. 5 is a cross-section taken on line 5-5 of FIG. 4;

FIG. 6 is a fragmentary cross-section on line 6-6 of FIG. 4; and

FIG. '7 is a similar view of a modified embodiment.

\ DESCRIPTION OF THE PRED EMBODIMENT Fig. I shows a temperature distribution profile, typical for a particular model of gas turbine eng'ne, along the span of a turbine blade from the hub or root end to the tip. The lowest temperature encountered during operation is represented by the left side of the graph, and occurs at the blade tip. The temperature rises rapidly from the tip toward the middle section of the blade, then drops off toward the root. It is to be understood that Fig. l is illustrative only of a typical condition, and specific parameters are not given, since they vary with the design of the engine and blades, the number of stages in the turbine, and the conditions of operation. Also, though the temperature difference from the coolest region of the span to the hottest is shown typically in the illustration as being of the order of 600 F ,such difference will vary with the factors mentioned above, and may in some cases be much greater.

In Fig. 2 there is shown a graphic representation of a typical variation of external gas pressure around a rotor blade in the region around the midsection, approximately halway between the root and the tip. A cross-section of a blade B is shown schematically, surrounded by a curve P in dotted line, the varying distance of curve P from the surface of the blade representing the variation in pounds per unit area of the external gas pressure surrounding the blade. Similar cross-sections taken at the root and at the tip would differ somewhat from the cross-section at the middle portion, as well as from each other. Again, Fig. 2 is to be understood as illustrative only of pressure variations which may occur, specific parameters de pending on such factors as mentioned above in connection with temperature.

Figs. 3, 4, and 5 shows various views of a rotor blade 11 constructed according to the invention. Such a blade comprises a solid strut member 12 having a root l3 and a tip portion 14. Both the concave side (Fig. 3) and the convex side (Fig. 4) of the blade strut are provided on the surface thereof with a plurality of longitudinal or spanwise lands l6 and a plurality of transverse or chordwise lands 117, which together define a plurality of generally discrete recesses 18 on each side of the strut. Although the blade shown is provided with five recesses across the chordwise direction on each side of the blade, and three rows of recesses in the spanwise direction, it will be understood that the number and sizes of the recesses will in each case be selected according to the design and operating conditions of a given engine, in accordance with variations in temperature and pressure at various portions of the blade.

The trailing edge 20 of the strut stops somewhat short of the final dimension of the blade, and is provided with one or more tapered projections 19 which stiffen and support the trailing edge of the permeable sheathing or skin 21 with which the strut is covered. The sheath is attached to the lands and to the periphery of the tip portion as by welding or brazing, and may be formed of any suitable porous material. As examples of such material, powdered metal or ceramic pressed to the desired shape and dimensions and sintered, as is known in the art. However, particularly suitable materials for the skin are metal fabrics, composed of fine filaments compressed and sintered together. Such metal fabrics are known in the prior art, and in one form may comprise a plurality of layers of woven mesh, assembled in laminar form and rolled or otherwise compressed to the desired thickness and porosity, and sintered or brazed together. Another satisfactory porous metal fabric may be obtained by winding a plurality of layers of a continuous filament on a mandrel and then rolling and sintering. This is also known in the art.

Above the root portion 13 by means of which the blade is mounted on the turbine rotor, there is provided a blade shelf 22, of the general form common to such blades. The underside of the shelf portion above the root is coved out on each side of the blade to form groves 23 extending in the chordwise direction. Such grooves receive the supply of cooling air from the rotor. Air supply passages or bores 24 extend through the shelf, communicating between the groove and each of the recesses 18 immediately adjacent to the shelf. Such bores may be drilled through the shelf from the upper side by conventional machining means where sufiicient clearance exists, or they may be formed by electron beam drilling. The bores may vary in size from one to another and on either side of the blade in accordance with the amount of cooling air to be distributed to various portions of the blade. At the leading and trailing edges of the blade the bores do not necessarily communicate directly with the grooves 23, owing to the overhang of the shelf 22 beyond the chordwise extent of the root portion 13 at both the leading the trailing edges.

In FIG. 7 there is shown another method of positioning the bores, designated as 24a. In a case where the clearances are too restricted to allow convenient manipulation of equipment for boring straight through the shelf, the bores 24a may be made angularly from the groove 23 on one side of the blade to recesses 18 on the opposite side, staggering the position of the bores so that they do not run into each other from opposite sides.

The transverse lands 17, extending across the surface of the strut 12 in the chordwise direction, are interrupted by cuts or apertures 26 between the row of recesses 18 next to the root and the center row, and by apertures 27 between the center row and the tipmost row of recesses. In general, apertures 27 are smaller in cross-sectional area than the corresponding apertures 26. Thus, cooling air fed from below the blade shelf 22 through bores 24 into the innermost row of recesses 13 will be metered in correct amounts through apertures 26 into the middle row of recesses, and again metered through apertures 27 into the outermost row of recesses, resulting in a pressure drop at each aperture. On the other hand, the centrifugal pumping action of the blade rotation tends to increase air pressure toward the tip end of the blade, so that each associated series of bores 24 and apertures 26 and 27 must be sized in relation to each other to discharge the desired amount of cooling air through the porous skin over each of the recesses 18. The tip end of the blade being closed, all cooling air supplied through bores 24 bleeds through the skin from the underlying recesses, proportionately cooling each portion of the blade surface in the amount required by the conditions of temperature and external gas pressure to which it is exposed.

In some designs it is also desirable to feed one or more of the recesses 18 from a similar recess which is adjacent in the chordwise direction, rather than from a recess which is nearer the root. In this case the longitudinal lands 16 may be interrupted by apertures 28 into the next chordwise recess.

What is claimed is:

1. A transpiration cooled turbine rotor blade, mountable on a turbine rotor having provision for delivering cooling air to the radially inner ends of the turbine blades, comprising in combination:

a. a solid strut member having a root portion for mounting on the rotor, a blade shelf positioned radially outwardly from the root, and a generally airfoil shaped portion extending radially outwardly from the shelf, the airfoil portion having on the surface thereof a plurality of spanwise and chordwise raised lands defining generally discrete recesses on the airfoil portion,

b. a porous sheath having capillary passages therethrough surrounding the airfoil portion and forming a blade surface and attached to the lands and defining generally discrete cooling air chambers with the strut recesses,

c. the air chambers having a generally rectangular outline with the longer dimension in the spanwise direction and being disposed in chordwise rows across the strut with at least three such rows of air chambers between the root and the tip end of the blade, the rows being separated by the chordwise lands,

(1. the strut member having on each side thereof a groove between the root and the shelf for reception of cooling air from the rotor, and the shelf having bores therethrough communicating with the grooves and with the air chambers adjacent to the shelf,

e. the chordwise lands having metering apertures therethrough to interconnect the air chambers on each side of the chordwise land,

. the cooling air being subject to centrifugal pumping action by the turbine rotor and the blades, the shelf bores being of larger cross-section than the radially inmost metering apertures, and the metering apertures of each row of air chambers being successively smaller in the radially outward direction such that a portion of the cooling air bleeds through the porous sheath overlying each air chamber and a further portion is metered through the chordwise land apertures to successively outward chambers, the centrifugal increase of air pressure toward the radially outward direction being compensated by a pressure drop at each successive aperture of smaller crosssection.

2. The combination recited in claim 1, wherein the bores through the shelf communicate between the groove and the rootmost recesses on the same side of the strut.

3. The combination recited in claim 1, wherein the bores through the shelf are angularly disposed to communicate between the groove on one side of the strut and the rootmost recesses on the other side. 

1. A transpiration cooled turbine rotor blade, mountable on a turbine rotor having provision for delivering cooling air to the radially inner ends of the turbine blades, comprising in combination: a. a solid strut member having a root portion for mounting on the rotor, a blade shelf positioned radially outwardly from the root, and a generally airfoil shaped portion extending radially outwardly from the shelf, the airfoil portion having on the surface thereof a plurality of spanwise and chordwise raised lands defining generally discrete recesses on the airfoil portion, b. a porous sheath having capillary passages therethrough surrounding the airfoil portion and forming a blade surface and attached to the lands and defining generally discrete cooling air chambers with the strut recesses, c. the air chambers having a generally rectangular outline with the longer dimension in the spanwise direction and being disposed in chordwise rows across the strut with at least three such rows of air chambers between the root and the tip end of the blade, the rows being separated by the chordwise lands, d. the strut member having on each side thereof a groove between the root and the shelf for reception of cooling air from the rotor, and the shelf having bores therethrough communicating with the grooves and with the air chambers adjacent to the shelf, e. the chordwise lands having metering apertures therethrough to interconnect the air chambers on each side of the chordwise land, f. the cooling air being subject to centrifugal pumping action by the turbine rotor and the blades, the shelf bores being of larger cross-section than the radially inmost metering apertures, and the metering apertures of each row of air chambers being successively smaller in the radially outward direction, such that a portion of the cooling air bleeds through the porous sheath overlying each air chamber and a further portion is metered through the chordwise land apertures to successively outward chambers, the centrifugal increase of air pressure toward the radially outward direction being compensated by a pressure drop at each successive aperture of smaller cross-section.
 2. The combination recited in claim 1, wherein the bores through the shelf communicate between the groove and the rootmost recesses on the same side of the strut.
 3. The combination recited in claim 1, wherein the bores through the shelf are angularly disposed to communicate between the groove on one side of the strut and the rootmost recesses on the other side. 